The present invention relates to a laser beam machining process for annealing workpieces with high reliability, high throughput, high uniformity, and a high production yield. More particularly, the invention relates to a method of laser annealing various materials including amorphous semiconductor materials, semiconductor materials of low crystallinity equivalent to amorphous semiconductor materials, metal materials, insulator materials, and various materials whose crystallinity has been severely deteriorated by ion irradiation, ion implantation, ion doping, or other similar method. Also, the invention relates to a method of doping a material with an impurity element by high temperatures created by laser irradiation.
In recent years, researches on low-temperature semiconductor fabrication processes have been earnestly conducted, because it is necessary to form semiconductor devices on an insulating substrate made of glass or the like or on an insulating coating formed on the semiconductor substrate and for other reasons. To fabricate these semiconductor devices, it has been necessary to thermally treat them. For example, in order to thermally crystallize a semiconductor coating which takes an amorphous state or a low crystallinity equivalent to the amorphous state, or to reduce unpaired electrons, or dangling bonds, in insulating films and semiconductor films, a thermal treatment performed at approximately 1000xc2x0 C. is needed.
However, where devices are formed on a glass substrate, it is necessary that the glass substrate withstand such high-temperature thermal treatment. Where semiconductor devices are formed on a semiconductor substrate, i.e., plural layers of semiconductor are formed, if the lower layer of devices has conductive interconnects of a low-melting metal, then it is not possible to perform a high-temperature treatment.
Accordingly, methods (including laser annealing) of creating a requisite local high-temperature state by laser irradiation in such a way that neither the substrate nor other conductive interconnects are damaged have attracted attention as ideal low-temperature processes. Especially, irradiation of short laser pulses less than 1 xcexcsec is an ideal method because other portions are hardly affected by conduction of heat. Among others, the use of an excimer laser emitting ultraviolet radiation has been considered to be most practical, because ultraviolet radiation is efficiently absorbed by many materials and because a large energy can be obtained.
However, severe laser processing conditions have heretofore existed. In consequence, laser processing techniques are far from stable techniques and do not provide sufficiently high reliability. Hence, it has generally been considered that laser processing techniques will never be put into practical use.
It is an object of the present invention to provide a laser processing technique which is an improvement over the prior art laser processing techniques and makes it possible to obtain stable requisite characteristics.
It is another object of the invention to provide a laser treatment method which can be applied to low-temperature semiconductor fabrication processes.
Other objects and features of the invention will appear in the course of the description thereof, which follows.
A laser processing method in accordance with the present invention comprises the steps of:
lasing a laser pulse having a pulse width w by a lasing device; and
amplifying said laser pulse by exciting a laser amplifier after 0.5 W to 5 w since said lasing step.
The laser pulse is irradiated to a surface to be processed through the laser amplifier. For example, the laser pulse is irradiated to a silicon semiconductor containing hydrogen at 1 volume % or more through the laser amplifier.